Oxiranes are valuable chemicals and are useful in a variety of end use applications. Epichlorohydrin, for example, is an oxirane and a valuable chemical commodity used extensively to make epoxy resins on a commercial scale. Currently, a “chlorohydrin” process is employed for manufacturing epichlorohydrin. The process begins with the chlorohydrination of allyl chloride by reaction with an aqueous dispersion of chlorine in water. This process forms an isomeric mixture of 1,2- and 1,3-dichlorohydrin, which is subjected to dehydrochlorination in caustic solution to yield epichlorohydrin. The chlorohydrin process is used to make over 95% of epichlorohydrin produced globally, but this known process suffers from the disadvantages of producing high levels of chlorinated organic compounds and salt in waste streams, and of producing large amounts of waste water.
There are several known processes in the art that use peroxide, such as hydrogen peroxide (H2O2), to produce an oxirane, including epichlorohydrin. Such processes are described in: Clerici et al., “Epoxidation of Lower Olefins with Hydrogen Peroxide and Titanium Silicalite,” Journal of Catalysis, 1993, 140, 71-83; U.S. Pat. No. 7,323,578; EP Patent Application Publication No. 1993/0549013 A1; Pandey et al., “Eco-friendly Synthesis of Epichlorohydrin Catalyzed by Titanium Silicalite (TS-1) Molecular Sieve and Hydrogen Peroxide,” Catalysis Communications, 2007, 8, 379-382; Chinese Patent Application No. CN 200710039080.1; Zhang et al., “Effects of Organic Solvent Addition on the Epoxidation of Propene Catalyzed by TS-1,” Reaction Kinetics and Catalysis Letters, 2007, 92(1), 49-54; Li, et al., “Epoxidation of Allyl Chloride to Epichlorohydrin by a Reversible Supported Catalyst with H2O2 Under Solvent-Free Conditions,” Organic Process Research & Development, 2006, 10, 876-880; Patent application PCTUS/08/080, titled “Process for epoxidizing olefins with hydrogen peroxide using supported oxo-diperoxo tungstate catalyst complex”; and U.S. Pat. No. 6,288,248 B1.
For epoxidizing some olefins, such as allyl chloride, using a peroxide reaction catalyzed by a titanium silicalite, it is well known that methanol is a necessary component of the peroxide reaction to obtain high activity and/or selectivity. Generally, methanol must be used in large excesses in the known processes. This results in the formation of byproducts from the reaction of methanol and water, which is solubilized in the organic phase by methanol, with an oxirane. It is estimated that the use of these large quantities of methanol would result in the construction of large towers and the consumption of a large amount of energy for the purification of the oxirane product if produced on a commercial scale. Additionally, a titanium silicalite-1 (TS-1) catalyst used under these conditions would deactivate in a matter of hours; and subsequently, would have to be fully regenerated by calcination. Furthermore, the high concentration of methanol promotes the formation of by-products through the reaction of the oxirane product with methanol.
Epoxidation systems generally require higher temperatures in addition to increased methanol concentrations. Higher temperatures typically decrease selectivity and result in lower yield of the desired oxirane. That is, increased temperatures can result in increased hydrolysis and/or solvolysis of the epichlorohydrin to byproducts such as, for example, monochlorohydrin.
Some of the problems of the known processes described above may be summarized as follows:
(1) High levels of methanol must be separated from the oxirane product and recycled which creates a high energy use and associated high costs for the process and can lead to high levels of by-products.
(2) High reaction temperatures can cause hydrolysis and/or solvolysis of the oxirane and form undesired byproducts, thereby decreasing the selectivity of the desired oxirane.
It is desired to provide a system and a process for preparing an oxirane product that can be operated at reaction conditions that do not have the problems of the above described processes; that still maintains a high catalyst activity; that increases the selectivity of the reaction; and that extends the lifetime of the catalyst without the need for any additional components which would have to be removed in a subsequent downstream process.